Relationship between clod surge occurrences over East Asia and expansion of polar vortex induced by upper-level blocking

Abstract

The present study has investigated the characteristics of the upper-level circulation and thermodynamical properties associated with the cold surge which induces the cold period over East Asia for one month from early December 2005 to early January 2006. The cold surge is caused by the upper-level blocking originated from the North Pacific. The upper-level blocking leads to the expansion of the Siberian High and the intrusion of the polar vortex toward East Asia. While strong decreasing trend of temperature is coincided with the annual cycle in December, the resulting lower-tropospheric anomalous wind and steep meridional temperature gradient in East Asia induced strong cold advection, which brought very cold continental air to East Asia and led to cold weather that lasted for one month.